More details can be found on:
http://dev.mysql.com/doc/relnotes/mysql/5.5/en/news-5-5-52.html
http://dev.mysql.com/doc/relnotes/mysql/5.5/en/news-5-5-51.html
http://dev.mysql.com/doc/relnotes/mysql/5.5/en/news-5-5-50.html